1. Field of the Invention
This invention relates generally to a removable implanted device that includes a sensor for measuring blood flow and other vessel characteristics. In particular the present invention relates to an encasement and a support structure to house such an implantable device.
2. Description of the Related Art
After certain medical conditions have occurred or certain medical procedures have been performed, it is often desirable to monitor blood flow through various veins or arteries, especially those in close proximity to the heart. For example, monitoring the flow of blood out of a patient""s aorta immediately following heart surgery can provide doctors with very valuable information.
Various devices have been designed to obtain blood flow information by making appropriate measurements. One device includes a transducer mounted within a housing. When attached to a blood vessel, the transducer utilizes the Doppler effect to monitor blood flow and the A- or M-mode to monitor the diameter of the vessel. The housing has a plurality of cutouts, with one or more release wires extending through the housing as illustrated in U.S. Pat. No. 5,205,292. The wires are releasably coupled to a front wall of the device and are exposed outside of the housing through the cutouts. These wires allow for the releaseable attachment of the device to a patient""s aorta.
A tube is coupled to the proximal end of the housing and extends out of the corpus of the patient. The necessary electrical/data connections made to the device are contained within the tube and provide the appropriate signals to monitoring equipment. The above mentioned release wires also extend through the tube to a point where they are accessible by the surgeon.
In use, the surgeon makes an incision into the patient. The housing of the device is positioned on the appropriate blood vessel, and sutures are used to connect the vessel to the housing via the exposed portions of the release wire. In other words, the exposed portions of the release wire provide anchoring points for the device. With the tube extending out of the corpus, the implantation wound is then sutured. The data lines are connected and patient information is transmitted to the monitoring equipment.
When specific blood flow data is no longer needed, the surgeon locates the portions of the release wires which extend out of the tube and retracts them. This causes a separation of the release wires from the front wall of the housing. As the wires are pulled backwards, they slide through the cutouts, thus releasing the sutures. Once the device is completely free, the surgeon can pull it out of the corpus by retracting the tube. Because the device is so small, it can exit through the opening left for the tube, and hence the surgeon need not create or reopen a wound in order to remove it. This represents a tremendous advantage in patient care, in that the corpus does not have to be needlessly and repeatedly opened to obtain blood flow measurements.
The housing and the transducer must be extremely small in order to be effective. As stated above, the device must unobtrusively sutured to various blood vessels and then removed through a surgical wound. It is critical that the wound remain as small as possible and that it not be unnecessarily disturbed. Obviously, making many of these components as small as possible, while also remaining operable, is often a complicated task. All materials and part configurations need to be optimized so as to meet all of the aforementioned goals. Also, manufacturing challenges need to be accounted for to insure an operating product can be fabricated without incurring exorbitant costs.
In order to be operable and effective, the transducer must be positioned at a specified angle with respect to the major axis of the vessel. Typically, this angle is accomplished by configuring the housing such that a predetermined angle is maintained between the transducer and the bottom of the housing. This is a difficult manufacturing step because the housing is made from compliant silicone. When the transducer is placed into the housing it is difficult to align properly. The most obvious method of fabricating an appropriate housing is to first mold a housing and then have the transducer attached thereto. In the context of this device, this is not an acceptable process as too many variables can be introduced. Specifically, a layer of adhesive is used to attach the transducer. This adhesive introduces a layer of material below the transducer. It is virtually impossible to insure that the layer of adhesive has parallel surfaces, and is free of air bubbles. The presence of either air bubbles or unparallel surfaces can effect the operation of the device.
If the transducer is being attached to a surface of the housing, it is then possible for the surface to be deformed. A deformation in the surface can also adversely effect the operation of the device.
Even if properly aligned, it is difficult to maintain this arrangement as the silicone housing sets. As such, the data obtained may potentially be skewed because of an unnoticed misalignment.
Additionally, the appropriate placement and retention of the release wires creates another manufacturing challenge. As can be appreciated, the release wires must be sufficiently retained within the housing so that suturing will hold the housing in place. Concurrently, the release wires must be sufficiently releaseable so they can be easily withdrawn at an appropriate point in time.
Again, one obvious way of manufacturing a housing which includes these release wires is to take the above discussed preformed housing, drill appropriate passage ways through the housing, and insert the release wires therethrough. However, these drilled holes are typically sized larger than the release wire itself, thus eliminating the natural ability of the housing to retain the release wires. In this configuration, the release wires are thus prone to slide out of the housing when being sutured. If this occurs, the device becomes virtually unusable as the measurements cannot be relied upon.
Another way of manufacturing a housing which includes these release wires is to take the above discussed preformed housing and pierce the release wires through the housing appropriately. This is prone to manufacturing inconsistencies which result in stress or strain on the compliant housing, unequal gripping force by the housing on the wires, ripping of the compliant housing, or improper placement of the wires.
As such, there exits a need to provide an easily removable implant containing a transducer securely and accurately fixed at a predetermined angle with respect to the surface of the implant contacting the wall of the vessel. There also exists a need to provide an implantable device which will maintain and position release wires in a consistent and predictable manner to accommodate appropriate retention of the device while also accommodating desired releaseability.
The present invention includes a structurally supportive shuttle member having a planar shelf which is offset at a predetermined angle from the main axis of the shuttle. A transducer is then mounted on the shelf, and as such, maintains the same predetermined angle. A cavity exists immediately behind the shelf and opposite the transducer. Acoustical backing material is placed in the cavity to enhance transducer operation. The various electrical components and connections required to operate the transducer are then placed within the space remaining in this cavity, beside the acoustical backing material. Connection to the actual transducer is made via conductive flex tapes which pass through appropriate openings in the shuttle.
Initially, the shuttle assembly will have three struts extending outwardly from its main body segment. The struts are used to provide support alignment and anchoring points for the shuttle during the assembly process. Initially, the transducer is mounted to the shelf and the various electrical connections are made. Next, acoustic backing material is placed in the cavity behind the transducer. The assembly is then insulated with parylene and plated with a gold shield. Release wires are then placed parallel to the major axis of the shuttle and are run through a coil stop that is located adjacent to one end of the shuttle. With all of these components properly in place, the shuttle is ready for encasement.
A housing is injection molded around the shuttle and its attached components. While this molding is used to produce the housing, it is more of an encasement than classical xe2x80x9chousing.xe2x80x9d The housing is formed so as to provide cutouts that provide the necessary suture points. That is, the portions of the release wire exposed through the cutouts accommodate sutures when attached to a patient. Portions of the struts extend out through the housing, and continue to support the assembly until the silicone solidifies. Once the silicone solidifies the extended portions of the struts and one end of the release wires are severed. Lastly, final assembly operations are completed such as placing all associated wiring into a protective tubing. At this point, a properly configured implantable device has been fabricated and is ready to be utilized.
It is an object of the present invention to provide a functioning transducer mounted within a structurally sound housing, wherein an angle of the transducer with respect to a lower wall of the housing is fixed.
It is another object of the present invention to provide a shuttle that can be used during the manufacture of an implanted device which utilizes an ultrasound transducer to measure certain characteristics of the body""s function.
It is yet still another object of the present invention to configure the shuttle so that it provides structural support to the housing, once completed.
It is still another object of the present invention to provide an easily manufacturable ultrasound transducer device which includes a shuttle that can support and properly align the components of an implanted device to enhance operation. This includes proper alignment of the transducer itself and appropriate positioning of connections and other acoustic materials. The use of this shuttle also provides for protection of the transducer during manufacturing.
It is yet another object of the present invention which provides for the appropriate retention of release wires to insure they stay in place during suturing, while also easily release when desired.
It is still yet a further object of the present invention to provide an implantable device wherein the electrical and mechanical connections are made without impeding the acoustical performance of the transducer.
It is another object of the present invention to provide a shuttle assembly for an implantable device wherein the shuttle includes a cavity for containing acoustical backing material to further enhance the operation of a transducer.
It is still another object of the present invention to electrically shield the components at an implantable device so that patient safety is assured and so that the components function properly.
It is a further object of the present invention to encase the electrically shielded components of an implantable device in a silicone housing.